The present invention relates to windings for dynamoelectric machines such as induction motors, and more particularly to windings for motors of relatively large horsepower and low voltage ratings.
While the usefulness of the present invention is not necessarily limited to any particular type or size of machine, it is particularly suitable for induction motors of relatively large horsepower and low voltage. In motors with horsepower ratings of about 200 horsepower or more at 230 volts, or 400 horsepower or more at 460 volts, the flexibility of design is severely limited because the field strength of the winding can be adjusted only in quite large steps. The reason for this is that windings for motors in these sizes, even with the maximum number of parallel branches possible for a given number of poles, require a relatively small number of turns per coil such as from two or six or seven turns. The smallest change in field strength that can be obtained in the design of such a winding by adjusting the number of turns per coil is therefore relatively large. For example, if a winding having three turns per coil does not give the desired field strength, the smallest change that can be made with a conventional winding design is the subtraction or addition of one turn per coil, so that the coils would have to be changed either two or four turns. A two-turn coil would provide a 50 percent stronger field than the original three turns while a four-turn coil would yield a 33 percent weaker field. Such an adjustment, in either direction, is a very coarse adjustment and makes it very difficult or impossible to obtain the desired field strength in many cases, thus undesirably limiting the flexibility of design.